...and you like it

A Very Simple And Easy Way To Reduce Comment Spam

Another option is to simply remove the web interface for comments and
only allow comments via the Comment API.

I have a hunch that most of the comment spam comes from people who
stumble on my site via the web. Most people who post via the CommentAPI
are using an aggregator and are thus subscribed to my site, or were
referred by another subscriber.

UPDATE: I may be confusing Comment Spam with Comment Graffiti. As
far as I can tell, I do not have any comments from any automated
sources, nor comments advertising products on my site. The "spam" I have
seems to merely be comments by random people who occasionally write
offensive comments.